we have actually gone the opposite way and switched to using syslog
for logging purposes some time ago, with no performance issues.
syslog files are easily read by a lot of applications out there. We have
been using rsyslog for aggregating logs from multiple servers, splunk
for analysis purposes and pgfouine for routine reports.
I would be very surprised if logging had a significant overhead any method
you choose. there's probably something very wrong with your setup if this
is the case.
just another dimension, Michael